Protective action of oxalic acid in relation to ascorbic acid against its oxidation by the ascorbic acid oxidase

Abstract

1. Oxalic acid has a definite protective action on ascorbic acid in its oxidation by ascorbic acid oxidase, an enzyme whose active group contains copper; this action is best revealed at pH 4.5. 2. Oxalic acid exerts also its protective action on ascorbic acid oxidation by copper; the comparison between the oxidative effect of copper oxalate and that of copper sulphate shows that the latter is much more intense. 3. The protective action of thiourea exerts itself in the oxidation by copper though less intensively than that of oxalic acid but it does not reveal itself in the oxidation by ascorbic acid oxidase. 4. The protective action of oxalic acid in the oxidation of ascorbic acid by the ascorbic acid oxidase suggests a new field of investigation in the branch of knowledge of those substances, not identified up to the present, which, in natural substrata, protect the ascorbic acid against such an oxidation.